The present disclosure relates generally to the field of power supplies for information handling systems, and more particularly to techniques for efficiently controlling a direct current to direct current (DC-DC) converter used in alternating current (AC) to direct current (DC) isolated power supplies.
As the value and use of information continues to increase, individuals and businesses seek additional ways to acquire, process and store information. One option available to users is information handling systems. An information handling system (‘IHS’) generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
It is typically required that power supplies providing power to the IHS, or components thereof, be isolated. That is, the AC/DC power supply output needs to be isolated from its input. Switching regulators such as a pulse width modulator (PWM) based controller have been widely used to cross the ground boundary between the primary and secondary side of a transformer for efficiently providing the isolated power output. However, it is difficult and costly to control switches referenced to the ground on the primary side in order to control the voltage output on the secondary side. By definition, this requires feedback of the voltage output on the secondary side to be translated to switch action on the primary side, while maintaining isolation between the primary and secondary sides.
Traditional AC/DC power supplies have utilized flyback converters with feedback elements such as optical (‘opto’) couplers and transformers to accomplish the isolation. However, opto couplers tend to have variable gains, which make their performance difficult to predict and control. As a result, they are prone to component failures, thereby having lower reliability. Gate drive and current sense transformers improve the accuracy and reliability but are more costly.
In a flyback converter, the primary winding of the transformer supplies energy to the magnetic core during the on-time of the primary side switch. During the off-time of the switch, the magnetic core delivers energy to the secondary side. Traditionally, two types of operational modes are typically used in flyback converters—Continuous Current Mode (CCM) or Discontinuous Current Mode (DCM). In the DCM mode, the primary side switch is turned on only when the secondary current has reached zero. In CCM mode, the primary side switch is turned on when secondary current is still above zero. As an example of a flyback converter based on a DCM device, iWatt Corporation, 90 Albright Way, Los Gatos, Calif. 95032-1827, USA, provides an iW2201 controller capable of DCM control. A product specification sheet published by iWatt Corporation, and entitled, ‘iW2201 Digital Offline Power Supply Controller’, Preliminary Data, Revision 1.7, describes one such isolated AC/DC power supply for powering the IHS and is incorporated, herein, by reference.
However, many traditional AC/DC power supplies based on the flyback converter design and utilizing the DCM may not be usable in power applications in which the secondary current may never reach zero. Also, DCM based control typically limits the power output of the AC/DC power supply and is less efficient. For the same output power, the peak current and the equivalent root mean square (RMS) current in CCM are lower than those in DCM operation. Thus, the conduction loss on the primary switch and secondary rectifier diode is less in the CCM compared to that in DCM, thereby increasing the total efficiency of the power supply.
Therefore, a need exists for improved power output and efficiency of isolated power supplies providing power to the IHS. More specifically, a need exists to develop tools and techniques for improving power output, efficiency and accuracy of flyback converters. Accordingly, it would be desirable to provide tools and techniques for an improved flyback converter providing isolated power to an IHS absent the disadvantages found in the prior methods discussed above.